1. Field of the Invention
The present invention generally relates to a refrigerant transporting hose and particularly to such hoses suitable for providing piping for car coolers, air conditioners and the like which are employed in automotive vehicles.
2. Related Art Statement
Referring to FIG. 2, there is shown a known hose for transporting or conducting a refrigerant such as Freon (fluorohydrocarbon). The hose has a three-laminated or layered structure consisting of an inner and an outer rubber tube 101, 103 and a reinforcing fiber layer 102 interposed between the inner and outer tubes 101, 103. The inner rubber tube 101 is formed of acrylonitrile-butadiene rubber (NBR), chlorosulfonated polyethylene rubber (CSR) or the like, the reinforcing fiber layer 102 is formed of polyester fiber, vinylon fiber (polyvinyl alcohol synthetic fiber) or the like, and the outer rubber tube 103 is formed o ethylene propylene diene rubber (EPDM), chloroprene rubber (CR) or the like. Reference numerals 115 designate spiking holes which are formed through the outer rubber tube 103 so as to communicate the reinforcing fiber layer 102 with outside space. The spiking holes 115 serve to relieve a portion of the refrigerant that has permeated the inner rubber tube 101, into the outside space, thereby preventing the hose from being swollen due to the refrigerant otherwise being trapped between the intermediate fiber layer 102 and the inner and/or outer rubber tubes 101, 103. Consequently, the hose is free from the problem of separation or peeling of each of the three laminates (two tubes and one layer) from the others due to the trapped refrigerant. Being formed of rubber material except for the reinforcing fiber layer 102, the hose has a high flexibility. Accordingly, the hose can be handled with ease, for example to provide piping. Furthermore, the rubber hose has an excellent seal characteristic, so that the hose is connected to a joint such as a nipple with high gas tightness. Rubber materials, however, have a comparatively high gas permeability, that is, a comparatively low resistance to gas permeation therethrough. Therefore, the rubber hose suffers from the problem of leakage of the refrigerant gas conveyed therethrough (especially where Freon whose molecular weight is comparatively low is used as the refrigerant).
Referring to FIG. 3, there is shown another known refrigerant transporting hose including an innermost layer 204 formed of a polyamide resin, such as nylon 6, which has a high resistance to gas permeation. The innermost resin layer 204 and a rubber layer 205 formed of a rubber material such as NBR disposed outside the resin layer 204, corresponding to the inner rubber tube 101 of the hose of FIG. 2. This hose further includes a reinforcing fiber layer 202 formed on the outer surface of the rubber layer 205 and an outer rubber tube 203 formed on the outer surface of the reinforcing fiber layer 202. Reference numerals 215 designate spiking holes similar to those 115 of the hose of FIG. 2. Having the innermost resin layer 204 formed of nylon or other polyamide resins that have a high resistance to gas permeation, the hose does not allow leakage of the refrigerant even if Freon with a comparatively low molecular weight is used as the refrigerant. However, the hose has a comparatively low flexibility because of the rigidity of the polyamide resin constituting the resin layer 204. Accordingly, it is not easy to handle the hose, for example, to provide piping for a refrigerant-using device or apparatus. Moreover, the prior art hose suffers from the problem that the polyamide resin layer 204 is deteriorated or damaged due to metallic ions and/or metallic salts developed from metallic piping. Furthermore, although the resin layer 204 and rubber layer 205 of the hose of FIG. 2 are bonded to each other with satisfactory bonding strength by an adhesive which typically contains a phenolic resin or a mixture of a phenolic resin and an epoxy resin, the adhesive layer becomes considerably rigid after being cured. Accordingly, the cured adhesive layer is low in impact resistance, whereby the adhesive layer has a high tendency to be fractured or broken upon exertion thereto of bending stress. When the adhesive layer is fractured, the resin layer 204 may be fractured together therewith because the resin layer 204 is in close contact with the adhesive layer. Accordingly, where the prior art hose is used in a condition wherein the hose is subject to bending stress, there is the possibility that the resin layer 204 is fractured together with the adhesive layer due to bending stress, thus leading to leakage of the refrigerant conducted through the hose.
As is apparent from the foregoing, none of the conventional refrigerant transporting hoses are satisfactory in quality.